1. Field of the Invention
The present invention relates to the field of direct conversion receivers for wireless communication.
2. Prior Art
High IIP2 (second order input intercept point) and low quadrature error are important requirements for direct conversion receivers to avoid distortion of the desired signal at low frequencies when converting directly from RF to baseband frequencies. In that regard, note that the IM2 (second order intermodulation) products also appear at zero IF. The IIP2 and quadrature error of current art mixers is generally not sufficient to make zero IF receivers possible without special calibration techniques. These techniques are undesirable because: (a) they may create a DC component which could block/overload the baseband, (b) they complicate and/or delay the start-up of the chip and end product (e.g. cellular phone), (c) they only work with a dedicated baseband chip, and (d) the performance over time and temperature may not be stable.